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UNIDENTIFIED STORM-PETRELS, PUERTO MONTT, CHILE, FEBRUARY, 2009


Jim Dowdall, Dublin, Ireland

Seamus Enright, Kerry, Ireland
Kieran Fahy, Wexford, Ireland 
Jeff Gilligan, Oregon, USA
Gerard Lillie, Oregon, USA
Michael O’Keeffe, Kerry, Ireland

INTRODUCTION

In early February 2009 our party of four Irish and two United States birders embarked on an exciting twelve day sea-birding voyage from Valparaiso, Chile south around Cape Horn and then north to Buenos Aires, Argentina, taking in various land stops along the route. 

Using the local field guide as reference (Jaramillo et al, 2003) we had noted Valparaiso’s position near the southern edge of the expected range for many Humboldt Current seabirds.  So, in order to maximize our seabird list a number of us decided to take in a pelagic off Valparaiso a couple of days prior to joining our ship.  On the pelagic we encountered a number of storm-petrels which at the time we found very puzzling.  They differed subtly from Wilson’s Storm-Petrels Oceanites oceanicus familiar to us all from the Northern Hemisphere.  The features appeared intermediate between Wilson’s and Elliot’s (White-vented) Storm-petrel Oceanites gracilis, including quite a delicate “jizz”, a relatively narrow wing base and a noticeably pale under-wing panel.  Many also displayed a lightly mottled vent/lower belly suggestive of Elliot’s. We considered Elliot’s a remote possibility off Valparaiso so we were keen to put a name to these birds.  After some research we concluded that these must be “Fuegian” Wilson’s Storm-petrel O. o. chilensis.  Such was the interest sparked by these birds that we began to closely inspect all storm-petrels thereafter.  This soon paid off! 

On February 4th, following a very rewarding day’s land-based birding at Alerce Andino National Park we re-boarded our ship and began journeying south from the city of Puerto Montt through Seno de Reloncaví.  Very soon we were encountering our first storm-petrels of the day.  Seamus Enright was the first to comment on the extent of white shown by these birds.  It was soon apparent that all the birds which we could see well showed lots of white on the vent/belly and on both the upper-wing carpal area and under-wing greater coverts.  This pattern was inconsistent with any known taxon  - once again we found ourselves puzzled by storm-petrels in Chilean waters.  With the light beginning to fade some of us hastily tried to capture images of these birds as we all tried to record what details we could from our perch high up on the bow of the ship. 

DESCRIPTION

By sunset we had counted approximately 50 storm-petrels in Seno de Reloncaví.  All of those photographed and observed well appeared to be of the same form.  Unfortunately the viewing conditions precluded a detailed examination. What follows is a description based on field observations backed up by photographic evidence. 

Most striking was the extent of white in the plumage, suggestive initially of one of the Fregetta storm-petrels.  However a number of features appeared to rule out that option, including the extent of dark on the flanks and the prominent carpal bar.  The birds appeared in fact to be Oceanites Storm-petrels, similar or perhaps slightly stockier than the chilensis Wilson’s Storm-petrels which we had been encountering further north.  The whitish upper-wing and under-wing panels appeared more striking than on any chilensis we had been observing.  The white on the rump appeared to wrap completely around the vent/lower belly, though from photographic evidence it is hard to rule out the presence of perhaps some dark feathering on the sides and centre of the vent.

DISCUSSION

These observations raise a number of tantalizing questions.  

Why have these birds apparently gone undocumented until now?  

Since highlighting our observation it transpires that visiting birders have seen similar birds in these waters and from the ferry crossing to Chiloé Island, not far from Puerto Montt (A. Jaramillo, R. Matus and P. Harrison pers. comm.).  While compiling this paper we were amazed to discover that Peter Harrison (pers. comm..) first encountered these birds in circumstances similar to our own, whilst working aboard the tour vessel M.V. Lindbald Explorer out of Puerto Montt in 1983/84.  Harrison has seen these birds many times in the intervening years.  On two occasions, Harrison remarks he “was lucky enough to have one land on the deck during the night and was able to give them careful scrutiny.  The wing measurements were 133mm and 135mm” respectively.  Using the only reference to hand (Murphy, 1936) and based on the measurements he had obtained, Harrison reached the conclusion these birds were chilensis.

It seems chilensis has a chequered history.  Robert Cushman Murphy in “Oceanic Birds of South America” (1936) describes how the taxa Oceanites oceanicus chilensis was inadvertently first published nomen nudum by W. B. Alexander in “Birds of the Ocean” (1928).  The taxon was later described in detail by Murphy (1936) and referred to as “Fuegian Petrel”, a new subspecies of Wilsons Storm-Petrel.  Subsequent to that, for reasons we have yet to establish, the taxon was “dropped” as a race of Wilson’s.  Until very recently only two races of Wilsons Storm-Petrel oceanicus and exasperatus were recognised in the literature, including by Harrison (1983, and in subsequent editions).
 
Interestingly in relation to Wilson’s Storm-Petrel, Harrison notes “Cape Horn birds may have pale vents (Naveen, pers. comm.).”  It would appear Ron Naveen was most likely referring here once again to chilensis which shows some pale mottling on the lower belly.  Onley and Scofield (2007) have recently re-established chilensis as a third race of Wilson’s.

How far do the Puerto Montt storm-petrels range?
 

Obviously we can only speculate.  One would however expect such relatively distinctive birds not to have gone unnoticed at a “well-watched” location like for example Valparaiso.  We did not see such well-marked birds anywhere else on our voyage.  Harrison (pers. comm.) has reportedly observed these birds near Puerto Montt, in the channel north of Chiloé Island and also in the Gulf of Penas, approximately 500km south of Puerto Montt.  The evidence therefore suggests these birds are relatively localized and sedentary in nature.

Acknowledgments

We would like to express our sincere thanks to Alvaro Jaramillo for his expert advice and encouragement during the preparation of this note.  We would also like to thank Peter Burke, Peter Harrison, Steve Howell, Santiago Imberti, Ricardo Matus, Mark Pearman, Christian Savigne, Fabrice Schmitt and Rodrigo Reyes and Chris Wilson.

Reference

Flood. R.L. and Thomas B. 2007. Identification of ‘black-and-white’ storm-petrels of the North Atlantic. British Birds 100:7 407-442.
Jaramillo, A., Burke. P. and Beadle, D. 2003. Birds of Chile. Helm Publications, London
Naveen, R. (1981) Storm Petrels of the World.  An Introductory Guide to their Identification. In: Birding 13(1981) S. 216-229.
Murphy, R.C. (1936). Oceanic Birds of South America, a study of species of the related coasts and seas, including the American quadrant of Antarctica based upon the Brewster-Sanford collection in the American Museum of Natural History.  The American Museum of Natural History. New York.
Onley, D. & Scofield, P. 2007. Albatrosses, Petrels and Shearwaters of the World. Helm Publications, London.
Harrison. P. 1983. Seabirds: An identification guide. Croom Helm, London.
Harrison. P. 1987. Seabirds of the World: a photographic guide. Helm Publications, London.
Pearman, M. 2000. First records of Elliot´s Storm Petrel Oceanites gracilipes in Argentina. El Hornero 15(2).
Robb. M., Mullarney. K and The Sound Approach. 2008. Petrels, Night and Day The Sound Approach
Saville, S., Stevenson, B., & Southley, I. 2003.  A possible sighting of an ‘extinct’ bird – the New Zealand Storm-Petrel. Birding World 16: 173-175.

(Text and images are all copyright of the authors).

 

Photos © Michael O'Keeffe

Fig. 1
Unidentified storm-petrels, Seno de Reloncaví, Puerto Montt, Chile, February 4th 2009.  The bird in the upper row of images may be a fresh juvenile while the lower two rows appear to depict adults in moult.  Note the extensive white on the vent and lower belly joining the rump.  There may be a slight suggestion of dark feathering on the vent.  The upper-wing and under-wing bars were both very prominent though these may appear slightly “exaggerated” here due to camera exposure.  We advise a degree of caution when analysing these slightly blurred, slightly over-exposed images. 
All photos Michael O’Keeffe

 

Digital sketch © Michael O'Keeffe

 

Fig. 2
Artist’s impression of the mystery Puerto Montt storm-petrel (bottom) together with chilensis and oceanicus/exasperatus Wilson’s Storm-petrels and both a typical and an atypical, well-marked example of Elliot’s Storm-petrel.  The Puerto Montt birds show less white on the belly and more white on the vent than typical Elliot’s Storm-petrels.  Elliot’s also shows a clear divide between belly and rump, along the femoral tract, although this may sometimes be faint or hidden.  chilensis is a daintier bird than either oceanicus or exasperatus and shows some plumage features suggestive of Elliot’s including pale mottling on the belly and a paler underwing panel.  Some indeed suspect chilensis may be closer to Elliot’s than Wilson’s. 
Digital sketch by Michael O’Keeffe.

 

Map of S America showing route of voyage

 

Fig. 3
Map of Southern South America showing the route of our voyage.  Within 24 hours of leaving Valparaiso we had left the expected range of many Humboldt Current species including Elliot’s Storm-Petrel.  On the 3rd day of the trip we encountered unidentified storm-petrels in Seno de Reloncaví, soon after departing Puerto Montt (see inset).